Inerting system for fuel tanks and the like

ABSTRACT

An inerting system which prevents fire and explosion within an aircraft fuel tank by maintaining the O2 concentration in the vapor space thereof at less than 10 percent by volume which is below the flammable limit. This system is in addition to the known inerting system wherein an inert gas such as N2 in the fuel tank vapor space dilutes and vents O2 liberated from the fuel as during ascent of the aircraft and pressurizes the tank a during descent of the aircraft to prevent entry of air. The present inerting system contemplates scrubbing of the fuel in the tank during flight of the aircraft by circulating the fuel through a mixing nozzle having its suction port communicated with a source of supply of inert gas such as N2 thus to liberate O2 dissolved in the fuel for venting through the tank vent.

United States Patent [151 3,693,915 [451 Sept. 26, 1972 Ulanovsky [54]INERTING SYSTEM FOR FUEL TANKS AND THE LIKE [72] Inventor: Jack M.Ulanovsky, Newport Beach,

Calif.

[73] Assignee: Parker-Hanniiin Corporation,

Cleveland, Ohio [22] Filed: Jan. 28, 1971 [21] Appl. No.: 110,536

[52] US. Cl. ..244/135 R [51] Int. Cl. ..B64d 37/00 [58] Field of Search..244/135 R [56] References Cited UNITED STATES PATENTS 3,229,446 l/l966Sebastian et al. ..244/135 R 3,467,349 9/1969 Gautier ..244/135 RPrimary Examiner-Evon C. Blunk Assistant Examiner-Douglas D. WattsAttorney-Oberlin, Maky, Donnelly & Renner 5 7] ABSTRACT An inertingsystem which prevents fire and explosion within an aircraft fuel tank bymaintaining the 0 concentration in the vapor space thereof at less thanl0 percent by volume which is below the flammable limit. This system isin addition to the known inerting system wherein an inert gas such as Nin the fuel tank vapor space dilutes and vents O liberated from the fuelas during ascent of the aircraft and pressurizes the tank a duringdescent of the aircraft to prevent entry of air. The present inertingsystem contemplates scrubbing of the fuel in the tank during flight ofthe aircraft by circulating the fuel through a mixing nozzle having itssuction port communicated with a source of supply of inert gas such as Nthus to liberate O dissolved in the fuel for venting through the tankvent.

14 Claims, 2 Drawing Figures PATENTED I973 3,693,315

1 I I I I I 1 I1 I I I I I I I I I I I I I I I I I I I I I I I I III.

INVENTOR.

JACK M. ULA/VOVSKY ATTORNEYS INERTING SYSTEM FOR FUEL TANKS AND THE LIKEBACKGROUND OF THE INVENTION tank pressure, as during descent of theaircraft.

However, hydrocarbon fuels as employed in aircraft typically dissolvegases including from the air in proportion to the gas partial pressuresat the air-fuel interface. Therefore, as tank pressure decreases duringascent, the fuel becomes supersaturated with the gases, that is, thefuel contains more gas than it can hold in equilibrium. When dissolvedgases become supersaturated by reduction of pressure on'the fuel, thegases will eventually come out of solution and rise into the vapor spaceabove the fuel; however, they do have a tendency to remain in solutionfor extended periods of time depending on the degree of supersaturationand the degree of agitation of the fuel. Thus, the release of gases fromfuel during and after climb is dependent on such variables as theattained altitude, buffeting of the aircraft by air turbulence, degreeof fullness of the tank which affects the extent of sloshing, etc.Therefore, the timing of release of the gas in any particular flight isnot predictable. Furthermore, the concentrations of the gases evolvedfrom fuel by reduction of pressure is dependent on the partial pressuresof the various dissolved gases and their solubility coefficients in thefuel. These factors are such that when gases are evolved fromhydrocarbon fuel that has been supersaturated with air, the 0concentration in the vapor space may exceed 30 percent, and therefore,merely preventing air from entering the fuel tank will not assure safetyagainst fuel tank explosion. It is also necessary to deal with the gasesdissolved in the fuel which will otherwise evolve therefrom as high 0,concentration gases during and after ascent.

SUMMARY OF THE INVENTION In the fuel tank inerting system constitutingthe present invention not only is an inert gas deployed in the vaporspace of the fuel tank to prevent air from entering the tank, butadditionally, dissolved O, is removed from the fuel during flight andespecially during the climb phase as tank pressure decreases, wherebythe 0 concentration in the fuel tank vapor space may be maintained at asafe level of percent or less 0, concentration so as not to propagateflame or explosion.

Herein, dissolved O, is removed from the fuel during flight bycirculating the fuel in the tank through a mixing nozzle which has itssuction port communicated with an inert gas supply source, wherebyintimate mixing of the inert gas and the fuel in the mixing nonleeffects scrubbing of the fuel to liberate O, therefrom.

The present invention also contemplates the provision of a control valvewhich in one operating position communicates the inert gas supply sourcewith the suc- .t ion port of the mixing nozzle and which in anotheroperating position cuts off the supply of inert gas and communicates thesuction port of the mixing nozzle with the fuel tank vapor space tomaintain the suction port and inert gas flow restrictor free of fuel forinstantaneous mixing action when the control valve is moved to said oneoperating position.

The inerting system herein also includes an inert gas tank pressurizingsystem which maintains tank pressure above ambient pressure duringdescent of the aircraft to prevent crushing of the tank by increasingambient pressure and also to prevent entrance of air into the vaporspace thereby to maintain a low 0, concentration in the vapor spaceinsufficient to support combustion.

Other objects and advantages of the present invention will appearhereinafter.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view of apreferred embodiment of the present fuel inerting system.

FIG. 2 is a cross section view of the mixing nozzle.

DISCUSSION OF THE INVENTION The reference numeral 1 in the drawingdenotes an aircraft fuel tank such as a wing tank, for example, into thevapor space 2 of which is supplied an inert gas such as N, through theconduit 3 and fog nozzle 4 leading to a gas supply source 5 which mayinclude a dewar, not shown, containing the inert gas in liquid form andcontaining suitable regulating valves to maintain predetermined pressurein the tank 1. The inert gas supply source 5 may be controlled by adifierential pressure sensing device 6 for supply of inert gas throughthe fog nozzle 4 into the vapor space 2 when ambient pressure exceedstank pressure by a predetermined amount, say, 0.1 psi as when theaircraft is descending.

Thetank l is provided with a vent valve 7 for outflow of venting gasesso that the inert gas present in the tank 1 maintains a maximum pressuredifferential between the vapor space 2 and the decreasing ambientpressure as when the aircraft is climbing. The vent valve 7 may haveprovision for inflow of air into the vapor space 2 as during descent ofthe aircraft in the event that the inert gas supply is exhausted or thatthe inert gas supply system 5 becomes inoperative thus to preventcrushing of the tank 1 during descent of the aircraft when ambientpressure increases.

The tank 1 has a fuel inlet valve 9 to which a fueling nozzle 10 isadapted to be coupled to refuel the tank. The inerting system ispreferably so arranged that when the aircraft has landed after a flightin which the inerting system has been utilized to pressurize the tank 1with inert gas, the pressure in the tank 1 may be between say 0.25 and0.75 psi above ambient pressure. Should the aircraft be parked for anextended period of time the pressure differential may decrease to alower value due to temperature changes or other reasons. When thepressure has decreased to a lower value such as 0.125 psi a regulatorvalve (not shown) in the supply source 5 will open so that inert gaswill flow into the tank 1 via conduit 3 and nozzle 4 to bring the tankpressure up to 0.25 psi above ambient pressure, whereupon the valveaforesaid will then close. Such an arrangement is shown for example inUS. patent application 71 1,020 filed Mar. 6, 1968, now US Pat. No.3,590,559 granted July 6, 1971 To effect scrubbing of the fuel in thetank 1 during the flight of the aircraft, especially during the climbphase, the fuel pumping system 11 not only supplies fuel from tank 1 tothe feed line 12 leading to the aircraft engines but also circulatesfuel in the tank 1 through a mixing nozzle 14 which has its suction port15 selectively communicated with the N, supply source 5 or with thevapor space 2 via the conduit 16, solenoid operated control valve 17,and conduit 18 or conduit 19. A gas flow restrictor means 20 is alsoconnected to the suction port 15.

When the solenoid 21 of valve 17 is energized as by control of adifferential pressure sensing device 22 that senses a predetermined dropin tank pressure as compared with a reference pressure during climb ofthe aircraft in the manner described in the above mentioned patentapplication, valve 17 assumes the position shown in FIG. 1 and N fromsource 5 flows through conduit 18, valve 17, conduit 16, gas flowrestrictor means 20, and suction port 15 for intimate mixing with thefuel being pumped through the mixing nozzle 14 thereby scrubbing thefuel and liberating 0, therefrom. The liberated mixed with N risesthrough the fuel to ullage space where it may further mix with the N,therein, sufficient N being within the ullage and/or introduced fromsupply so that the 0, content of the ullage is always maintained at lessthan percent. When the solenoid 21 is de-energized, still under thecontrol of pressure differential device 22, valve 17 shifts to close thesupply conduit 18 and open communication between conduits 16 and 19so'that the suction port iscommunicated with the vapor space 2. As thefuel continues to be pumped through the mixing nozzle 14 the resultingsuction in the port 15 draws the gas mixture from vapor space 2 throughline 19, valve 17, line 16 and restrictor 20 into mixing nozzle 14 whereit mixes with fuel passing through the nozzle and is discharged into thebody of fuel in the tank. This keeps fuel out of said port 15, saidrestrictor means 20, and conduit 16 that would otherwise enter the samefrom nozzle 14 when the connection of line 16 to the N supply 5 is cutoff. Thus, when the solenoid 21' is again energized, there is no delayin supplying of N from 5 to nozzle 14 and hence in the commencement ofthe scrubbing of the fuel. Otherwise, if fuel had entered the conduit16, the N from supply 5 would first have to force the fuel through thegas flow restrictor means 20 and port 15 before scrubbing action wouldoccur.

The system is adaptable for use with a plurality of fuel tanks, in whichcase line 16 has a branch 24 leading to another restrictor 20 and nozzle14 in another tank (not shown), and the nozzle 14 in such other tank maybe supplied with fuel by another pump 11 in such other tank, or by abranch connection with pump 11 in tank 1. In such case the restrictors20 for the various nozzles 14 are selected with proper orifice sizes soas to balance the flow of N or vapor therethrough in any desired manner;

I claim:

1. An inerting system for an aircraft fuel tank and the like comprisingmixing means having an outlet in the tank and having a suction port;means for inducing flow of fuel through said mixing means; inert gassupply means; and control valve means operative to selectivelycommunicate said suction port with said supply means to mix inert gaswith the fuel as it flows through said mixing means thus to liberate 0from the fuel or with the vapor space of the tank to maintain saidsuction port free of fuel during continued operation of said inducingmeans.

2. The system of claim 1 wherein said tank has vent means for flow ofventing gases from said vapor space.

3. The system of claim 1 wherein said mixing means has gas flowrestrictor means at saidsuction port.

4. The system of claim 1 wherein said supply means has conduit meanscommunicated with said vapor space independently of said control valvemeans to pressurize said tank with inert gas to maintain apressure closeto ambient pressure in said tank as during descent to the aircraft andto dilute the O concentration in said vapor space.

5. The system of claim 1 wherein said suction port is disposed at alevel below the fuel level in said tank; and wherein said control valvemeans has ports communicated with said supply means, said suction port,and said vapor space.

6. The system of claim 5 wherein said mixing means has gas flowrestrictor means at said suction port also disposed below the fuel levelin said tank.

7. In an aircraft fuel tank inerting system wherein an inert gas supplymeans is communicated with the vapor space of said tank to pressurizesaid tank and to prevent entry of air thereinto as during descent of theaircraft, the improvement which comprises mixing means having a fuelpressure inlet, an outlet which opens into said tank, and a suction portbetween said inlet and outlet; pump means for inducing flow of fuelthrough said mixing means; control valve means operative to selectivelycommunicate said suction port with said supply means to mix inert gaswith the fuel as it flows through said mixing means thus to liberate 0from the fuel or with said vapor space to maintain said suction portfree of fuel during continued operation of said pump means; and ventmeans in said vapor space through which gases, including 0 released fromthe fuel, are vented.

8. The system of claim 7 wherein said mixing means has gas flowrestrictor means upstream of said suction port also disposed below thefuel level in said tank.

9. The system of claim 7 wherein said mixing means comprises a mixingnozzle.

10. An aircraft fuel tank inerting system comprising a fuel tank havinga vent means; an inert gas supply means; first means for conductinginert gas from said supply means into the vapor space of said tank topressurize said tank and to prevent entry of air into said tank throughsaid vent means as during descent of the aircraft; second means forconducting inert gas into said tank as afuel-inert gas mixture in whichthe inert gas is effective to liberate 0 from the fuel into said vaporspace for venting through said vent means; said second means comprisingmixing means through which fuel in said tank is circulated and valvemeans operative to conduct inert gas to said mixing means either fromsaid supply means or from said vapor space.

11. The system of claim 10 wherein said mixing means comprises a mixingnozzle having a suction port which is communicated with said supplymeans or with said vapor space by operation of said valve means.

12. The system of claim 10 wherein said mixing means has an outlet forfuel-inert gas mixture which is submerged in the fuel in said tank.

13. The system of claim wherein pump means is operatively connected tosaid mixing means to circulate fuel in said tank through said mixingmeans.

14. The system of claim 11 wherein a gas flow restrictor means isdisposed at the suction port of said 5 mixing nozzle.

1. An inerting system for an aircraft fuel tank and the like comprisingmixing means having an outlet in the tank and having a suction port;means for inducing flow of fuel through said mixing means; inert gassupply means; and control valve means operative to selectivelycommunicate said suction port with said supply means to mix inert gaswith the fuel as it flows through said mixing means thus to liberate 02from the fuel or with the vapor space of the tank to maintain saidsuction port free of fuel during continued operation of said inducingmeans.
 2. The system of claim 1 wherein said tank has vent means forflow of venting gases from said vapor space.
 3. The system of claim 1wherein said mixing means has gas flow restrictor means at said suctionport.
 4. The system of cLaim 1 wherein said supply means has conduitmeans communicated with said vapor space independently of said controlvalve means to pressurize said tank with inert gas to maintain apressure close to ambient pressure in said tank as during descent to theaircraft and to dilute the O2 concentration in said vapor space.
 5. Thesystem of claim 1 wherein said suction port is disposed at a level belowthe fuel level in said tank; and wherein said control valve means hasports communicated with said supply means, said suction port, and saidvapor space.
 6. The system of claim 5 wherein said mixing means has gasflow restrictor means at said suction port also disposed below the fuellevel in said tank.
 7. In an aircraft fuel tank inerting system whereinan inert gas supply means is communicated with the vapor space of saidtank to pressurize said tank and to prevent entry of air thereinto asduring descent of the aircraft, the improvement which comprises mixingmeans having a fuel pressure inlet, an outlet which opens into saidtank, and a suction port between said inlet and outlet; pump means forinducing flow of fuel through said mixing means; control valve meansoperative to selectively communicate said suction port with said supplymeans to mix inert gas with the fuel as it flows through said mixingmeans thus to liberate 02 from the fuel or with said vapor space tomaintain said suction port free of fuel during continued operation ofsaid pump means; and vent means in said vapor space through which gases,including 02 released from the fuel, are vented.
 8. The system of claim7 wherein said mixing means has gas flow restrictor means upstream ofsaid suction port also disposed below the fuel level in said tank. 9.The system of claim 7 wherein said mixing means comprises a mixingnozzle.
 10. An aircraft fuel tank inerting system comprising a fuel tankhaving a vent means; an inert gas supply means; first means forconducting inert gas from said supply means into the vapor space of saidtank to pressurize said tank and to prevent entry of air into said tankthrough said vent means as during descent of the aircraft; second meansfor conducting inert gas into said tank as a fuel-inert gas mixture inwhich the inert gas is effective to liberate 02 from the fuel into saidvapor space for venting through said vent means; said second meanscomprising mixing means through which fuel in said tank is circulatedand valve means operative to conduct inert gas to said mixing meanseither from said supply means or from said vapor space.
 11. The systemof claim 10 wherein said mixing means comprises a mixing nozzle having asuction port which is communicated with said supply means or with saidvapor space by operation of said valve means.
 12. The system of claim 10wherein said mixing means has an outlet for fuel-inert gas mixture whichis submerged in the fuel in said tank.
 13. The system of claim 10wherein pump means is operatively connected to said mixing means tocirculate fuel in said tank through said mixing means.
 14. The system ofclaim 11 wherein a gas flow restrictor means is disposed at the suctionport of said mixing nozzle.